1. Field of the Invention
The present invention relates to flexible couplings with built-in damping and is of particular utility as incorporated in light aircraft engines. While the invention is of general utility in coupling a prime mover to a load, it is shown as incorporated in a reciprocating aircraft engine system.
For years torsional vibrations in light aircraft reciprocating engines have been a significant problem. The reason for this is that an aircraft engine must be light in weight, so it has no heavy flywheel to limit the torsional vibrations. While it is connected to a large propeller the effective inertia that the engine realizes is rather small because of the propeller's own flexibility. With no substantial flywheel attached to the engine's rotating system, torsional vibration problems are present. These include possible gear failures in the reduction gearbox and the accessory gears in a geared engine and in the accessory gears in a direct drive engine. Problems may also be present in the accessories attached to the engine, such as fuel pumps, alternators, compressors, hydraulic pumps and the like. The propeller is also affected by the engine's vibratory impulses. In fact, the propeller is one of the major contributors to the vibration problems. Since it has blade flexibility that can produce frequencies that coincide with the engine's frequencies, the problem is aggravated. The invention provides an improved solution to the problem.
2. Description of the Prior Art
Attempts have been made in the past to solve these problems by incorporating tuned counterweights on the engine's crankshaft to reduce the firing impulses produed by the engine. In some cases the necessity to control other frequencies by this type of counterweight makes the problem more difficult since there is sufficient room in the engine for only a limited number of weights.
This system of counterweights is generally effective in protecting engine parts, accessories and the propeller. However, they are relatively complicated in manufacture, heavy and expensive to produce, particularly if they are incorporated in a high speed, small four-cylinder engine.
Our U.S. Pat. No. 3,834,181 issued Sept. 10, 1974, entitled "Aircraft Engine Flexible Coupling" and assigned to Avco Corporation, represents one of the more advanced prior art types. A rotating input member is provided with radially inwardly extending discs. A concentric output member has radially outwardly extending discs alternately arranged in relation to the first-mentioned discs. Ring-like elastomer members are disposed between the metallic discs to provide elastic coupling and damping. Relative movement of the inner and outer members is limited by tooth and notch engagement.
In U.S. Pat. No. 2,394,405 to Schjolin the drive is via a torsionally elastic quill shaft. U.S. Pat. No. 2,738,660 to Gail shows an elastic quill shaft in combination with loosely mating splines between which damping fluid is introduced. U.S. Pat. No. 1,965,742 to Junkers shows a combination generally similar to that of Gail.
U.S. Pat. No. 3,263,450 to Condon illustrates the complexities which arise in the use of a torsion bar in combination with tooth and notch engagement between inner and outer sleeves for providing the damping effect. Particular attention is invited to the complex system for supplying and circulating the viscous damping fluid in the Condon structure.
In the system of the Happ et al. U.S. Pat. No. 2,910,843 inner sleeves and outer sleeves are in effect intercoupled by a plurality of metallic discs, dimple and cut-out formations providing for elasticity and looseness of play. Resilient synthetic materials are disposed between the discs.
The Geislinger torsional coupling has an outer drive member and an inner driven member and a number of leaf spring packs radially projecting from the driving member into slots in the driven member. The pockets between the leaves are filled with spacers.
The above discussed references are believed to be fairly representative of the more pertinent prior art.